On Fri, Nov 29, 2024 at 01:59:01PM +0100, David Hildenbrand wrote: > On 29.11.24 13:55, Lorenzo Stoakes wrote: > > On Fri, Nov 29, 2024 at 01:45:42PM +0100, David Hildenbrand wrote: > > > On 29.11.24 13:26, Peter Zijlstra wrote: > > > > On Fri, Nov 29, 2024 at 01:12:57PM +0100, David Hildenbrand wrote: > > > > > > > > > Well, I think we simply will want vm_insert_pages_prot() that stops treating > > > > > these things like folios :) . *likely* we'd want a distinct memdesc/type. > > > > > > > > > > We could start that work right now by making some user (iouring, > > > > > ring_buffer) set a new page->_type, and checking that in > > > > > vm_insert_pages_prot() + vm_normal_page(). If set, don't touch the refcount > > > > > and the mapcount. > > > > > > > > > > Because then, we can just make all the relevant drivers set the type, refuse > > > > > in vm_insert_pages_prot() anything that doesn't have the type set, and > > > > > refuse in vm_normal_page() any pages with this memdesc. > > > > > > > > > > Maybe we'd have to teach CoW to copy from such pages, maybe not. GUP of > > > > > these things will stop working, I hope that is not a problem. > > > > > > > > Well... perf-tool likes to call write() upon these pages in order to > > > > write out the data from the mmap() into a file. > > > > I'm confused about what you mean, write() using the fd should work fine, how > > would they interact with the mmap? I mean be making a silly mistake here > > write() to file from the mmap()'ed address range to *some* file. > Yeah sorry my brain melted down briefly, for some reason was thinking of read() writing into the buffer... > This will GUP the pages you inserted. > > GUP does not work on PFNMAP. Well it _does_ if struct page **pages is set to NULL :) Anyway let me go try this and see what happens... > > -- > Cheers, > > David / dhildenb >
